Method for cleaning filters

ABSTRACT

In a method and apparatus for cleaning filters, the cleaning is efficiently performed by selecting cleaning steps according to the degree of contamination of the filter media. The degree of contamination of the filter media is analyzed before the filter is carried into the cleaning apparatus. Filters with heavily contaminated filter media are subjected to pretreatment before the cleaning process is performed, and the filters with less contaminated filter media are directly subjected to the cleaning process. The cleaned filter is subjected to a restoration process before reuse.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of U.S. application Ser. No. 09/607,741, filed Jun.30, 2000 now U.S. Pat. No. 6,394,113.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for cleaningfilters, such as air intake filters, ventilation air filterscontaminated with dust and other particles, etc.

2. Description of the Related Art

Filters are used in various fields to remove dust and other particlesfrom fluid such as air. For example, medium performance filters are usedfor air passages in air conditioning systems in buildings or undergroundshopping malls, and are used in air intake lines of devices such aslocal gas turbine generators. These filters are used to remove salts,dust, oil particles, fibers and other substances (hereafter collectivelyreferred to as “contaminants”) from the air by collecting them on afilter media of resin fiber or other materials.

FIGS. 10a and 10 b show a perspective view of such filters. The filter Fshown in FIG. 10a has a filter media f with a corrugated non wovenfabric of resin fibers or of glass fibers, folded in parallel to thecorrugation in zigzag pattern and retained within a frame 51. The filterF shown in FIG. 10b has a filter media f folded in zigzag pattern withcorrugated separators f(a) inserted between folded filter media andretained within the frame 51.

As an apparatus for cleaning such filters, the applicant has filed apatent application of an ultrasonic cleaning apparatus (JapaneseLaid-Open Patent Publication No. Hei 9-276633). In this apparatus, acontaminated filter accommodated on a rack is conveyed by a handlingunit to an ultrasonic cleaning tank for cleaning, and a cleaned filteris rinsed in a rinse tank and returned to the rack.

However, filters F cannot always be cleaned under the same conditionbecause the degree of contamination of such filters varies according totheir conditions of usage and other factors. For instance, when allfilters are cleaned in the condition needed for cleaning heavilycontaminated filters, a considerable time loss occurs in the cleaning ofless contaminated filters.

On the other hand, when all filters are cleaned in the short period oftime needed for cleaning of less contaminated filters, sufficientcleaning effect is not obtained for the heavily contaminated filters,and cleaning of the internal portion of the filter media is sometimesdifficult.

Moreover, as filters F has a frame surrounding a complicated filtermedia, contaminants removed from the filter media tend to reattach onthe cleaned filter media, which sometimes makes difficult the completeremoval of contaminants.

It is therefore an object of the present invention to provide a methodand apparatus for cleaning filters in accordance with the degree ofcontamination.

SUMMARY OF THE INVENTION

In the filter cleaning method according to the present invention, thedegree of contamination of the filter media is analyzed to select thecleaning steps of the filter according to the degree of contamination.Heavily contaminated filters are subjected to pretreatment beforecleaning, while less contaminated filters are cleaned withoutpretreatment, and cleaned filters are subjected to a restoration processfor preventing decrease in thickness of the filter media after drying.The pretreatment can be performed by a method such as immersing thefilter in a pretreatment solution containing a detergent. Therestoration can be performed by a method such as immersing the filtermedia in a restoration solution containing a softener. In this way, thenecessity of performing pretreatment is determined according to thedegree of contamination, therefore, the heavily contaminated filtermedia is cleaned effectively by the addition of pretreatment before thecleaning, while the less contaminated filter media is cleaned in ashorter time. Moreover, by utilizing the restoration process after thecleaning, the capturing capacity of contaminants per filtering area isrestored to the capacity before the cleaning.

Heavily contaminated filters are preferably subjected to pretreatmentand to rinsing of the pretreatment liquid before the cleaning. Thecontaminants become easily removable by the pretreatment, and a greaterpart of the contaminants can be removed by the rinsing to significantlyenhance the effectiveness of the subsequent cleaning process.

In addition, the sterilization of filters for use in environments whichwill affect human beings can be performed continuously after therestoration.

Furthermore, by performing processes up to the cleaning and processesafter the cleaning in separate systems, the processes up to the cleaningwhich need longer time, and processes after the cleaning can beperformed independently, thus increasing the efficiency and reducing thetime needed for performing the cleaning operation.

Ultrasonic cleaning can efficiently remove contaminants within thefilter media.

The cleaning unit according to the present invention comprises, meansfor analyzing the degree of contamination of the filter media, means forarranging the filter in a predetermined location according to the degreeof contamination, means for conveying the filter from the predeterminedlocation, means for performing pretreatment when the filter isclassified as heavily contaminated, means for cleaning the filter; andmeans for restoring the filter media for preventing reduction ofthickness after the cleaning. With this filter cleaning method andapparatus, the degree of contamination of the filter media is firstanalyzed by the analysis means and classified according to previouslydetermined standards, and the filter is accommodated at thepredetermined location according to the classification. The heavilycontaminated filter is conveyed to the pretreatment process, and theless contaminated filter is conveyed directly to the cleaning process bythe conveying means. Then the filter media of the cleaned filter isrestored. Thus efficient cleaning operation can be performed byselecting the cleaning procedure according to the degree ofcontamination of the filter media. As a result, by the restoration afterthe cleaning, sufficient filtering capacity of the cleaned filter can berestored.

In addition, by providing the pretreatment rinsing means, the cleaningeffect can be increased because the contaminants have become easilyremovable by the pretreatment process and can be rinsed away before thecleaning. The pretreatment rinsing means provided by a pretreatmentrinse tank having a flow generating means for directing rinsing liquidtoward the filter media also enhances the filter cleaning effect.

Filters for use in environments that affect human beings can besterilized after the cleaning by the sterilization means which isprovided after the restoration of the filter media.

Furthermore, by separating conveying means into two separate systems,i.e. conveying means for conveying the filter in processes up to thecleaning of the filter, and conveying means for conveying the filter inprocesses after the cleaning, cleaning of the filters which need alonger time can be performed simultaneously with other processes such asa restoration process. As result, working efficiency is significantlyincreased thereby reducing the total work time.

In addition, by forming the cleaning means as an ultrasonic cleaningtank, in which the filter is immersed for a specified amount of time,the contaminants adhered on the filter media can be removed effectivelyby means of cavitation created by the ultrasonic waves.

Moreover, by conveying means which comprises a filter frame for holdingthe filter and a conveyor unit which holds the upper portion of thefilter frame while conveyed, the conveyor unit can be prevented frombeing wetted by the cleaning liquid during the pretreatment, cleaning orrestoration processes.

These objects as well as other objects, features and advantages of thepresent invention will become more apparent to those skilled in the artfrom the following description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of a filtercleaning apparatus according to the present invention;

FIG. 2 is a plan view of an example of a pretreatment rinse tank shownin FIG. 1;

FIG. 3 is a front view of the pretreatment rinse tank in FIG. 2;

FIG. 4 is a side view of the pretreatment rinse tank in FIG. 2;

FIG. 5 is a flow chart showing an example of analyzing the degree ofcontamination of filters to be conveyed into the filter cleaningapparatus shown in FIG. 1;

FIG. 6 is a flow chart showing processes up to a cleaning step in thefilter cleaning apparatus shown in FIG. 1;

FIG. 7 is a flow chart showing processes after the cleaning step of thefilter cleaning apparatus shown in FIG. 1;

FIGS. 8a and 8 b show a front view and a side view respectively of asecond preferred embodiment of a holding means of the conveyor unit inthe filter cleaning apparatus according to the present invention;

FIGS. 9a, 9 b and 9 c show a plan view, a side view and a perspectiveview, respectively, of the filter holding means in the conveyor unit inFIG. 8; and

FIGS. 10a and 10 b are perspective views of filters to be cleaned by thecleaning apparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a support frame 2 of conveyor unit C1 and C2 of afilter cleaning apparatus M is provided on a foundation 1 of rectangularplane shape. Conveyor units C1 and C2 movable in the direction X and Yare mounted on the top surface of the support frame 2. Racks 3 areprovided on the foundation 1 for temporarily accommodating a pluralityof filters to be cleaned and cleaned filters. The racks 3 are arrangedin a plurality of lows in the width direction (X direction) toaccommodate a plurality of filters F in longitudinal direction (Ydirection), and each accommodating location is previously numbered.

Transportation of filters to the rack 3 is performed by a transportingunit (not shown) such as a crane or a conveyor belt. The transportingunit is provided with filter analyzer means A for analyzing the degreeof contamination of the filter media to be cleaned. The degree ofcontamination of the filter media can be analyzed by such as measuring apressure drop by passing a gas through the filter media, or by measuringthe weight difference of the filter between a contaminated condition anda non-contaminated condition. The degree of contamination can also beanalyzed by measuring the thickness of the filter media, because thethickness of the filter media increases according to the amount ofaccumulated contaminants. Various other means can be employed foranalyzing the degree of contamination. The filter to be cleaned ispreliminary classified according to the degree of contamination by theanalyzing means.

On both lengthwise end portions of the foundation 1, a plurality oftanks are arranged for performing the respective steps of cleaningfilters F. In this embodiment, a pretreatment tank 4, a pretreatmentrinse tank 5 and a tank 6 a for ultrasonic cleaning unit 6 are arrangedin the front end portion (lower left portion of FIG. 1) of thefoundation 1. A rinse tank 7, a restoration tank 8 and a sterilizationtank 9 are provided in the rear end portion (upper right portion ofFIG. 1) of the foundation 1. In this embodiment, processes up to thecleaning, i.e., processes performed in the group of tanks 4, 5, and 6 a,and processes after the cleaning, i.e. processes performed in the groupof tanks 7, 8, and 9, can be performed in separate systems, and twoconveyor units C1 and C2 are provided for conveying filter F in eachrespective system.

Conveyor units C1 and C2 are mounted respectively on a rectangularconveyor frame 11 which is movable along rails 10 mounted on the topsurface of the support frame 2 in the Y direction. A conveyor cart 12 ismounted on the respective conveyor frame 11 and movable along rails 11 ain the X direction. The conveyor frames 11 are moved in the Y directionalong the rails 10 by drive units not shown, and the conveyor carts 12are moved along the conveyor frames 11 in the X direction by drive units13. Holding means are provided on the underside of respective conveyorcarts 12 for holding the filter F during transport and process. Theholding means in this embodiment is formed as a pair of conveyor arms 14to hold the filter F frame in widthwise.

The conveyor arms 14 are provided on the underside of the platform 16which is suspended under the conveyor cart 12 and is moved vertically bya drive motor 15, and adapted to move oppositely in widthwise with eachother by a drive motor 17. A holding plate 18 is provided between theconveyor arms 14 to hold filters F at a specified position in the liquidin the respective tank. A control panel 19 is provided for controllingthese units.

The pretreatment tank 4 is provided to facilitate removal ofcontaminants adhered to the filter media f. In this embodiment, thepretreatment tank 4 is a square vessel filled with an aqueous solutioncontaining detergent as a pretreating agent. By immersing the filters Fin the aqueous solution, the detergent penetrates into the boundariesbetween contaminants and fibers of the filter media f to facilitateremoval of contaminants and thereby enhance the cleaning effect in thesubsequent cleaning process by the cleaning unit 6.

The pretreatment rinse tank 5 is provided for rinsing away thecontaminants being made easily removable by the penetration of thedetergent in the pretreatment tank 4. FIG. 2 shows an example of a planview of the pretreatment rinse tank 5. FIGS. 3 and 4 show a front viewand a side view of the pretreatment rinse tank 5. In this embodiment, aflow generator 20 is provided as a flow generating means to facilitateremoval of contaminants.

The filter F is immersed in the water in a square vessel 5 a in thepretreatment rinse tank 5, and the flow generator 20 creates a waterflow directed toward both sides of the filter media f. Water flow iscreated on the surface of the filter media f by the water ejected fromnozzles 21 provided at lower portion of both sides of the filter mediaf. In this embodiment, two nozzles 21 are provided on each side to causewater flow to each respective face of the filter media f. The watersuctioned by a pump 22 through an intake pipe 23 provided at the bottomof the pretreatment rinse tank 5 is delivered through a pipe 24 to eachof the nozzles 21. In the figures, the water is shown as ejected fromall of the nozzles 21, but in the actual operation, the water is ejectedalternately, so that when the water is ejected form the nozzles 21 onone side, the ejection from the nozzles 21 on the other side is stopped.This is for the purpose of allowing a part of water to pass through thefilter media f for preventing recontamination of the other filter mediaside. With such rinsing, a part of water flow created by the nozzles 21can flow through the filter media f and promote removal of contaminantswithin the filter media f. The type of flow generator 20 can be selectedaccording to the size of the filter F and the thickness and shape of thefilter media f. A selector valve 24 a is provided on the pipe 24 toselect the water flow to eject from the nozzles 21 or to circulate tothe upper portion of the pretreatment rinse tank 5.

A water level sensor 25 is also provided to detect the drop of the waterlevel in the pretreatment rinse tank 5. When the drop of water level isdetected, the water is supplied through a supply pipe 26. In thisembodiment, the water is also delivered to the other tanks 4, 6 athrough the supply pipe 26. A drain pipe 27 is also provided.

The cleaning unit 6 is a unit that utilizes ultrasonic waves forremoving the contaminants stuck to the filter media f by a cavitationcreated by the ultrasonic waves in the cleaning liquid. The filter F isinserted from the open top of the square ultrasonic cleaning tank 6 a ofthe cleaning unit 6 and held upright in the cleaning liquid to directboth the upstream side and the downstream side of the filter media f ina horizontal direction, so that the filter media f is cleaned by theultrasonic waves generated by the ultrasonic oscillator 28 provided onthe upstream side or the downstream side of the filter F. The ultrasonicwave generated by the ultrasonic oscillator 28 creates effectivecavitation in the filter media f of the filter F held in the cleaningliquid. In this embodiment, the filter F and the ultrasonic oscillator28 do not move with respect to each other during the cleaning. Dependingon the type or other factors of the filter F, however, it is possible tomove either of them during cleaning. In this embodiment, the filter F isheld stationary at the predetermined location in the cleaning tank 6 aby the conveying arm 14 of the conveyor unit C1.

The filter media f is held in parallel to the ultrasonic oscillator 28to face each other in the ultrasonic cleaning tank 6 a. Therefore, afilter media f with large surface area can be cleaned effectivelyutilizing cavitation created by the ultrasonic waves passed through thefilter media f and reflected on the opposite wall.

The rinse tank 7 is adapted to wash away the reattached contaminantsonce removed from the surface of the filter media f by the ultrasoniccleaning unit 6. Similar to the pretreatment rinse tank 5, the rinsetank 7 also has flow generators 20 to remove contaminants once removedby the cleaning unit 6 and contaminants dropped from the filter media fand reattached on the filter F. By holding the filter F stationary inthis manner during removal of the contaminants, the reattachment ofcontaminants can be prevented.

The restoration tank 8 is adapted to restore filtering capacity bypreventing reduction of thickness of the filter media f due to theshrinkage after cleaning. The restoration tank 8 also has a square shapeand is filled with restoration liquid. Examples of the restoration agentused in the restoration tank 8 for restoring the filter media f includenonionic surface activators, positive ion surface activators and othersofteners. The kind of restoration liquid can be selected according tothe type and thickness of the filter media f.

The sterilization tank 9 is used for sterilizing the filter F after therestoration, and particularly for sterilizing filters of indoor orhousehold use to prevent pollution with germs in environments that mayaffect human beings. The sterilization tank 9 also has a square shape.Ozonized water and hypochlorous acid soda may be used as thesterilization medium.

FIG. 5 is a flow chart showing steps for analyzing the degree ofcontamination of the filter which is transported into the filtercleaning apparatus. FIG. 6 is a flow chart showing steps up to cleaningof the filter by the filter cleaning apparatus. FIG. 7 is a flow chartshowing steps performed after the filter has been cleaned by the filtercleaning apparatus. The following explanation is based on the embodimentshown in FIG. 1 in which the respective processes up to the filtercleaning and processes after filter cleaning are performed as separatesystems. In this embodiment, the filters F are classified in advanceaccording to the degree of contamination, and arranged at predeterminedlocations on the rack 3 according to the classification. The filters Farranged on the same rack 3 are adapted to be sequentially cleaned underthe same condition. Other selecting steps in the flow chart aredetermined by the data preliminary entered in the control unit.

As shown in FIG. 5, the filters F are transported into the filtercleaning apparatus M by transporting unit such as a conveyor belt (stepa). The degree of contamination of the filters F is measured by thefilter analyzer means A before the filters F are conveyed into thefilter cleaning apparatus M (step b). The measured result is recorded inthe control panel or the filters F are arranged at predeterminedlocations according to the measured result (step c). In this embodiment,the filters F are classified and arranged at the predetermined locationon the rack 3 according to the degree of contamination determined by thefilter analyzer means A. The conveyor units C1 and C2 are used as themeans for conveying the filters F from the transporting unit to the rack3. When the filters F to be cleaned have been placed at thepredetermined location on the rack 3, the cleaning process can bestarted (step d) as shown in FIG. 6.

Heavily contaminated filter F is taken out from the rack 3 (step e) bythe conveyor arm 14 of the conveyor unit C1, and if the filter F isclassified as heavily contaminated (step f) conveyed to the pretreatmenttank 4 according to the degree of contamination. In this embodiment, thefilter F is already classified as heavily contaminated, the filter F iscarried into the pretreatment tank 4 by the conveyor unit C1 in whichthe conveyor frame 11 moves in the Y direction along the rails 10, andthe conveyor cart 12 moves in the X direction along the conveyor frame11. Above the pretreatment tank 4, the filter F is dipped in thepretreatment liquid in the tank 4 by lowering conveyor arms 14. Thefilter F is held in the pretreatment liquid including detergent for apredetermined time period sufficient to allow the detergent to penetratethrough the entire surface of the filter media (step g). After thepredetermined time period, the filter F is removed from the pretreatmenttank 4 by lifting conveyor arms 14, and conveyed into the adjacentpretreatment rinse tank 5.

Above the pretreatment rinse tank 5, the filter F is dipped in the waterin the pretreatment rinse tank 5 by lowering conveyor arms 14, and thefilter F is held in the predetermined position, then, the water isejected from the nozzles 21 (FIG. 2) provided in the pretreatment rinsetank 5 to wash away the detergent on the filter media f and facilitatethe removal of the pretreated contaminants (step h). After thepredetermined time period, the filter F is removed from the pretreatmentrinse tank 5 by lifting the conveyor arms 14, and conveyed into theadjacent cleaning unit 6.

Above the cleaning unit 6, the filter F is dipped into the cleaningliquid in the cleaning tank 6 a by lowering conveyor arms 14. When thefilter F is held at the predetermined position in the cleaning tank 6 a,ultrasonic waves generated by the ultrasonic oscillator 28 detach thecontaminants stuck on the filter media f (step i). The heavilycontaminated filter F can be cleaned effectively, because thecontaminants comes off easily after the pretreatment. After thepredetermined time period, the filter F is removed from the cleaningunit 6 by lifting conveyor arms 14, and returned to the predeterminedlocation on the rack 3 (step j). In this embodiment, filter conveyingoperation and filter holding operation in a series of processes up tothe cleaning, i.e., step e to step j is performed by the conveyor unitC1 in a single system. By repeating operation of conveyor unit C1 inthis system, a large number of filters F can be cleaned efficiently.

As shown in FIG. 7, the cleaned filter F returned on the rack 3 is takenout by conveyor arms 14 of the other conveyor unit C2 (step k). Whenrinsing is required (step 1), the filter F is conveyed into the rinsetank 7. Above the rinse tank 7, the filter F is dipped into water in therinse tank 7 by lowering conveyor arm 14. As in step h, water is ejectedfrom the nozzles 21 provided in the rinse tank 7 to rinse away thereattached contaminants on the filter media f (step m). After thepredetermined time period, the filter F is removed from the rinse tank 7by lifting conveyor arms 14, and then the rinsed filter F is conveyedinto the adjacent restoration tank 8.

Above the restoration tank 8, the filter F is dipped into therestoration liquid in the restoration tank 8 by lowering the conveyorarms 14. Leaving the filter F in the restoration fluid for thepredetermined time period, the filter media f is restored (step n). Therestored filter F is removed from the restoration tank 8 by liftingconveyor arms 14, and if sterilization is required (step o), the filterF is then conveyed into the adjacent sterilization tank 9 and subjectedto sterilization process (step p). Filters F for use in the environmentwhere human beings work or livestock are kept, need sterilization in thesterilization tank 9. Filters F for use in industrial machinery orengines do not need sterilization.

The sterilized filter F is removed from the sterilization tank 9 bylifting conveyor arms 14, and the filter F is returned to thepredetermined location on the rack 3 (step q) by the conveyor unit C2.The series of conveying and holding operations after the cleaning offilters F is performed by the other conveyor unit C2. The conveyor unitC2 repeats the process from the step k to the step g above, therefore, alarge number of filters F can be cleaned efficiently. When the series ofoperations has been completed the cleaned filter F is returned to therack 3. After the predetermined time period necessary to dry, thecleaned filter F is brought out by a transporting unit such as aconveyor belt to the filtering unit to reinstall.

In this manner, the heavily contaminated filter F can be cleanedeffectively, by subjecting to pretreatment before performing ultrasoniccleaning by the cleaning unit 6. Moreover, in this embodiment, theoperation is efficiently performed in a short period of time byutilizing two separate conveyor units C1 and C2.

The cleaning operation for the less contaminated filter is performed byskipping the (steps g and h) as shown in FIG. 6. Also in this case, lesscontaminated filters F are classified in advance and arranged at thepredetermined location on the rack 3. The filter F is taken out from therack 3 by conveyor arms 14 of the conveyor unit C1 (step e), and thenconveyed directly to the cleaning unit 6 by the conveyor unit C1 whichmoves along the rails 10 in the Y direction, and the conveyor cart 12which moves along the conveyor frame 11 in the X direction.

Above the cleaning unit 6, the filter F is dipped into the cleaningliquid filled in the ultrasonic cleaning tank 6 a by lowering conveyorarms 14 for performing ultrasonic cleaning (step i). After thepredetermined time period, the filter F is removed from the cleaningunit 6 by conveyor arms 14 and returned to the predetermined location onthe rack 3 (step j). A series of conveying operation is performed by theconveyor unit C1 as a single system.

As shown in FIG. 7, the cleaned filter F returned on the rack 3 is thentaken out by conveyor arms 14 of the other conveyor unit C2 (step k). Ifrinsing is necessary (step 1), the remaining contaminant on the filtermedia f is rinsed away in the rinse tank 7 (step m). After rinsing inthe rinse tank 7, the rinsed filter F is then conveyed to the adjacentrestoration tank 8.

Above the restoration tank 8, the filter F is dipped into therestoration liquid filled in the restoration tank 8 by lowering conveyorarms 14. Leaving the filter F in the restoration fluid for thepredetermined time period, the filter media f is restored (step n). Ifthe sterilization is required (step o), the restored filter F isconveyed to the sterilization tank 9 to perform a sterilization process(step p). The sterilized filter F is removed from the sterilization tank9 and conveyed by the conveyor unit C2 to the predetermined location onthe rack 3.

In this manner, the less contaminated filter F can be cleanedefficiently in a short period of time because the filter media f can besubjected to ultrasonic cleaning by the cleaning unit 6 withoutpretreatment. The filters F having been cleaned by the series of stepsare kept at a suitable place for a certain time period needed to dry,and are transported by the transporting unit (not shown) to thefiltering unit for reinstall.

According to this embodiment, the degree of contamination is analyzed inadvance and the filter F are arranged at a predetermined location on therack 3 according to the degree of contamination. Consequently, the flowof the cleaning operation can be simplified by operating conveyor unitC1 such that the cleaning operation of filters F arranged at certainlocations on the rack 3 starts from the pretreatment tank 4, and thecleaning operation of filters F arranged at other locations on the rack3 starts from the cleaning unit 6. In addition, according to thisembodiment, the utilization of two conveyor units C1 and C2 greatlyreduces the operational time required to perform the series of cleaningoperations, because while the filter F to be cleaned is conveyed by oneconveyor unit C1 into the cleaning unit 6 to perform the time consumingcleaning process, the cleaned filter F on the rack 3 is conveyed byother conveyor unit C2 into the rinse tank 7 to perform rinsing andsubsequent process. As a result, the time required for the series ofcleaning operations can be reduced greatly by the simultaneousoperations of the two conveyor units C1 and C2.

The control panel 19 can be configured to monitor the temperature andquantity of the water in the cleaning unit 6 or to monitor contaminationof the cleaning fluid according to the type of the filter F or thedegree of its contamination.

In this embodiment, two conveyor units C1 and C2 are provided toefficiently clean filters, however, the conveying and holding operationof the entire cleaning process can be performed by a single conveyorunit when a small number of filters are cleaned. Thus the presentinvention is not intended to be limited to the embodiment describedabove.

FIG. 8 shows a second embodiment of the conveyor unit in the filtercleaning apparatus according to the present invention. FIG. 8a shows afront view and FIG. 8b shows a side view. FIG. 9 shows a filterretaining element of the conveyor unit shown in FIG. 8. FIG. 9a shows aplan view, FIG. 9b shows a side view and FIG. 9c shows a perspectiveview of the holding element. As shown in the figures, the filter F isretained to a filter retaining frame 29, and the retaining frame 29 isconveyed by the conveyor units C1 and C2 (FIG. 1).

As shown in FIG. 8a, the filter retaining frame 29 comprises a framebody 30 formed by frame members 30 a which surround both sides and thebottom of the filter F, a rail member 30 b which connects the upperportions of the frame members 30 a, hold members 30 c being movablealong the rail member 30 b; and suspension members 31 having latchingmembers 31 b which suspend the rail member 30 b at both sides of theframe member 31 a. The frame body 30 has a square shape in plan view asshown in FIG. 9a. The latching members 31 b can swing outward, and areswung downward when the rail member 30 is suspended such that both endsof the rail member 30 are inserted into latching holes 31 c (FIG. 9c) ofthe latching members 31 b from left and right sides to support the railmember 30 b, as shown in the two dotted chain lines in FIG. 8a.

With the filter retaining frame 29 of this configuration, the suspensionmember 31 is held by the platform 16 which is raised and lowered by thedrive motor 15 in the same mariner as the aforementioned conveyor unitsC1 and C2, so that the filter F is raised and lowered together with theframe body 30. Consequently, the filter F held by this filter retainingframe 29 can be processed without dipping the lower end portion of theconveyor unit such as conveyor arm 14 into the liquid in the tanks.Moreover, in this embodiment, the filter F is retained in suspendedcondition, the size of the tanks can be reduced widthwise making thewhole unit more compact

Adoption of this type of suspension means can be made in accordance withthe type of filter F and the cleaning method, and the present inventionis not intended to be limited to the preferred embodiment describedabove.

Numerous modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, this description is to be construedas illustratively only, and is provided for the purpose of teachingthose skilled in the art the best mode of carrying out the invention.The details of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention and all modificationswhich come within the scope of the appended claims are reserved.

What is claimed is:
 1. A method for cleaning a contaminated filterincluding a filter media comprising steps of: analyzing a degree ofcontamination of the filter media for selecting cleaning steps accordingto the degree of contamination; arranging said filter at a predeterminedlocation in a filter cleaning apparatus after classifying said filteraccording to the degree of contamination; taking out and conveying saidfilter from said predetermined location; performing pretreatment of afilter media classified as heavily contaminated; cleaning said filtermedia and returning it to a predetermined location; and restoring thefilter media for preventing the reduction of the thickness cleaning. 2.The method according to claim 1, further including steps of: taking outand conveying the cleaned filter from said predetermined location aftersaid cleaning step; and sterilizing said filter after said restoringstep.
 3. The method according to claim 2, wherein processes up to saidcleaning step and processes after said cleaning step are performed inseparate systems, utilizing conveying means provided in each step forconveying the filters.
 4. The method according to claim 1, wherein thecleaning step is performed by ultrasonic cleaning.